The present invention relates to a heavy duty radial tire, and more particularly to a reinforcing structure suitable for airplane radial tires.
In radial ply tires used under severe conditions such as high internal pressure, heavy load and high speed, that is, in the heavy duty radial ply tires, a higher durability is required in comparison with other types of tires.
Particularly in the heavy duty radial ply tires for airplanes, the bead portion is apt to be broken starting from the turned up end of the carcass ply or in the vicinity thereof by the stress accompanying the bending deformation of the bead portion caused by heavy load at takeoff and landing.
Therefore, in order to reinforce the bead portions, increasing the hardness of the bead apex, increasing the volume of the bead apex, and adding a cord reinforcing layer have been mainly employed.
However, if these means are employed, it becomes difficult to keep the generated heat at a low level, to lower the repeating stress, and to prevent ply separation, which rather increases the occurrence of bead damage.
Moreover, when the tire is used at a high speed, for example over 300 km/h, a standing wave is apt to be generated, and if a standing wave is generated on the tire, it leads the bead portions to complicated deformation, and as a result, the durability of the bead portions is significantly lowered.
It is, therefore, an object of the present invention to provide a heavy duty radial tire improved in bead durability under very severe conditions.